Several conventional valves possibly relevant to the present invention are known to the applicant and are listed in the tabulation below:
______________________________________ U.S. Pat. No. Issued Inventor ______________________________________ 2,324,464 20 July 1943 A. L. Parker 2,831,490 22 April 1958 W. H. Simcock 2,934,077 26 April 1960 J. C. Whiting 2,942,611 28 June 1960 W. C. Klank, Jr. et al 2,942,612 28 June 1960 W. C. Klank, Jr. 3,685,528 22 August 1972 J. L. Holland ______________________________________
All of these valves involve compromises made in view of often times conflicting design interests. Among these design interests are low cost, positive operation, avoidance of liquid slugging in venting use, and avoidance of air entrainment in liquid pickup use. Also, relative ease of maintenance, or the complete freedom from the need for maintenance, is highly desirable because these valves are often installed in inaccessible locations. Because these valves are intended for aerospace applications small size and light weight are very important. Unfortunately many of the conventional valves are relatively complex in their structure or are expensive to manufacture or difficult to maintain. Also some known valves are larger and/or heavier than is desired for use in aerospace applications. Also, under certain operating conditions certain of these conventional valves may allow liquid slugging from the vent when they are used to vent a tank, such as an oil tank, or they may allow entrainment of air when used to pick up a liquid fuel from a fuel tank.